The Role of Plant Growth Regulators in Modulating Root Architecture and Tolerance to High-Nitrate Stress in Tomato

Optimization, application effects and improved microecology of a composite microbial agent containing oyster shells

Oysters are one of the largest marine shellfish species worldwide. However, oyster shells are treated as waste, accumulating on coastal shores and seriously polluting the ecosystem. In this study, a composite microbial agent was developed using calcined oyster shell powder, Beauveria bassiana spore powder, and ecological chitosan. To release the active ingredients, oyster shells were treated by calcination. The optimal application ratio of the agent was determined by detecting tomato growth indicators. Application of the optimized agent to vineyards increased 100-grain weight, carotenoids, and total amino acids by 10.55%, 8.71%, and 29.40%, respectively. Further detection of soil microbial population changes showed that the application of the agent increased the abundance and diversity of soil microbial populations, promoting the metabolism of bacterial amino acids, polysaccharides. These findings suggest that the agent not only enhanced plant growth and fruit quality, but also enriched the diversity and abundance of soil microbial communities.

Biochemical and yield response of spring wheat to drought stress through gibberellic and abscisic acids

Drought stress significantly impacts wheat productivity, but plant growth regulators may help mitigate these effects. This study examined the influence of gibberellic acid (GA3) and abscisic acid (ABA) on wheat (Triticum aestivum L., CV: Giza 171) growth and yield under different water regimes. Using a split-plot design, we tested three drought levels as main plots: normal irrigation (80% field capacity), moderate drought (60% field capacity), and severe drought (40% field capacity). Subplots consisted of GA3 and ABA treatments at 100 and 200 ppm concentrations. Results showed that 200 ppm GA3 treatment enhanced multiple growth parameters under normal irrigation, including plant height (25-30% increase), leaf area (30-35% increase), and reproductive traits (40% increase in number of number of spikes, 35% increase in grains per spike). In contrast, ABA treatment at 200 ppm resulted in reduced plant height (35% decrease) and greater leaf area reduction (40% vs. 20% in control) under drought conditions. GA3 at 200 ppm also improved physiological parameters including catalase and superoxide dismutase activities, protein content, and proline accumulation. These findings demonstrate the distinct roles of GA3 and ABA in regulating wheat growth and stress responses, providing valuable insights for drought management in wheat cultivation.

Cerium oxide nanoparticles promoted lateral root formation in Arabidopsis by modulating reactive oxygen species and Ca2+ level

Roots play an important role in plant growth, including providing essential mechanical support, water uptake, and nutrient absorption. Nanomaterials play a positive role in improving plant root development, but there is limited knowledge of how nanomaterials affect lateral root (LR) formation. Poly (acrylic) acid coated nanoceria (cerium oxide nanoparticles, PNC) are commonly used to improve plant stress tolerance due to their ability to scavenge reactive oxygen species (ROS). However, its impact on LR formation remains unclear. In this study, we investigated the effects of PNC on LR formation in Arabidopsis thaliana by monitoring ROS levels and Ca2+ distribution in roots. Our results demonstrate that PNC significantly promote LR formation, increasing LR numbers by 26.2%. Compared to controls, PNC-treated Arabidopsis seedlings exhibited reduced H2 O2 levels by 18.9% in primary roots (PRs) and 40.6% in LRs, as well as decreased O 2 · - levels by 47.7% in PRs and 88.5% in LRs. When compared with control plants, Ca2+ levels were reduced by 35.7% in PRs and 22.7% in LRs of PNC-treated plants. Overall, these results indicate that PNC could enhance LR development by modulating ROS and Ca2+ levels in roots.

SlTrxh functions downstream of SlMYB86 and positively regulates nitrate stress tolerance via S-nitrosation in tomato seedling

Nitric oxide (NO) is a redox-dependent signaling molecule that plays a crucial role in regulating a wide range of biological processes in plants. It functions by post-translationally modifying proteins, primarily through S-nitrosation. Thioredoxin (Trx), a small and ubiquitous protein with multifunctional properties, plays a pivotal role in the antioxidant defense system. However, the regulatory mechanism governing the response of tomato Trxh (SlTrxh) to excessive nitrate stress remains unknown. In this study, overexpression or silencing of SlTrxh in tomato led to increased or decreased nitrate stress tolerance, respectively. The overexpression of SlTrxh resulted in a reduction in levels of reactive oxygen species (ROS) and an increase in S-nitrosothiol (SNO) contents; conversely, silencing SlTrxh exhibited the opposite trend. The level of S-nitrosated SlTrxh was increased and decreased in SlTrxh overexpression and RNAi plants after nitrate treatment, respectively. SlTrxh was found to be susceptible to S-nitrosation both in vivo and in vitro, with Cysteine 54 potentially being the key site for S-nitrosation. Protein interaction assays revealed that SlTrxh physically interacts with SlGrx9, and this interaction is strengthened by S-nitrosation. Moreover, a combination of yeast one-hybrid (Y1H), electrophoretic mobility shift assay (EMSA), chromatin immunoprecipitation-quantitative PCR (ChIP-qPCR), and transient expression assays confirmed the direct binding of SlMYB86 to the SlTrxh promoter, thereby enhancing its expression. SlMYB86 is located in the nucleus and SlMYB86 overexpressed and knockout tomato lines showed enhanced and decreased nitrate stress tolerance, respectively. Our findings indicate that SlTrxh functions downstream of SlMYB86 and highlight the potential significance of S-nitrosation of SlTrxh in modulating its function under nitrate stress.

Discontinuous low temperature stress and plant growth regulators during the germination period promote roots growth in alfalfa (Medicago sativa L.)

In high-cold regions, alfalfa is susceptible to cold damage during the seed germination. The effects of discontinuous low temperature stress and plant growth regulators (PGRs) on alfalfa were studied in response to the high day/night temperature differentials in the area. The experiments included seed germination, seedling cold tolerance and plant recovery. Variable temperatures (VT) of 0 °C/15 °C, 5 °C/20 °C and 10 °C/25 °C were set and seeds were soaked with alginate oligosaccharides (AOS), brassinolide (BR) and diethyl aminoethyl hexanoate (DA-6) during the germination period. Parameters such as seed germination and mean germination time (MGT), phenylalanine ammonia-lyase (PAL) activity and oligomeric proanthocyanidins (OPC) content of early seedlings, dry matter accumulation and root crown of the restored plants were analysed. The results showed that low variable-temperature (LVT) stress prolonged the MGT but had little inhibitory effect on germination percentage. Early seedlings adapted to LVT stress by regulating their own water and OPC content, PAL activity and other parameters. LVT induced early alfalfa seedlings to increase their underground biomass by shortening root length and increasing root diameter, and those that had accumulated more underground biomass had faster growth rates and higher total biomass when the ambient temperature rose. AOS also promoted an increase in root crown diameter and root dry weight. This research proved that LVT stress and AOS during the germination process can lead to better growth of alfalfa in high cold regions.